Method of producing galvanic coatings



Aug. 5, 1930. v. ENGELHARDT ET AL METHOD OF PRODUCING GALVANIC COATINGSFiled Feb. 9, 1926 ILVCIIZZEI'S" 15 WW Attorn/qys.

Patented Aug. 5, 1930 UNITED STATES PATENT OFFICE VICTOR ENGELHABDT, OFIBEBLIN-CHARLOTTENBEBG, AND KURT ILLIG, OF BERLIN- WILMERSDORF, GERMANY,ASSIGNOBS TO SIEMENS a HALSKE, AKTIENGESELL- SCHAFT, OF SIEHENSSTADT,NEAR BERLIN, GERMANY, A CORPORATION or GED- MANY METHOD OF PRODUCINGGALVANIO COATINGS Application filed February 9, 1926, Serial No. 87,020,and in Germany October 17, 1925.

The present invention relates to the production of galvanic coatings onbodies, es e- (ciall on narrow tubes. In obtaining dura le coatings itis often necessary--for example when producing a chromium coat1ngto workwith an electrolyte which attacks nearly a1 substances, especiallymetals in the unpolarized condition, giving rise to 1111 purities in theelectrolyte. In such case 1t 1s therefore necessary to use the hollowbody as the cathode and, furthermore, when making internal coatings, touse it as electrolyzer. Again, in the case of the production of coatingson comparatively narrow tubes,-there is present in the internal hollowspace of the tube only a small quantity of the electrolyte which, on thepassage of the electric current, is liable to become heated to boilingpoint by the J oules heat developed. The whirling of the liquidresulting in this case and the rising gas bubbles then make theproduction of a satisfactory inner coating for the tube impossible.

The invention relates to a process for ob- 2 viating the disadvantagesmentioned and to an apparatus that is es ecially advantageous for thecarrying out 0 this process, particularly for producing chromiumcoatings, but is also applicable to other electroplating processes inwhich difiiculties similar to those set forth above are experienced.

In carrying out the new method for producing galvanic coatings onbodies, the body to be coated is used as the cathode and brought into anelectrolyzer. According to the invention an anode arrangementcontinuously dipping into the electrolyte is moved with relation to thecathode body along those parts of the surface which are to be coated.The velocity of this movement is so chosen that the resulting coating isof the desired thickness at every point. It is immaterial to theinvention whether only the body or only the anode arrangement or bothparts be moved as long as there is a relative motion. The essentialadvantage of the new method with regard to other well-known methodsconsists in the fact that the newmethod may be employed for producingouter or inner galvanic coatings on bodies of any form, and especiallyon narrow tubes.

In the drawings there is shown an example of an apparatus for carryingout the new process. Figure 1 is a longitudinal section through theapparatus and Figure 2 is a section on the line AB of Figure 1. i

In an electrolyzgr orvelectrolytic vessel 1 that contains the electrolte 2 a hollow body 3 is arranged so as to be xed in position, forexample by being suspended by means of a wire 18, and is connected insuch'a manner that it will become the cathode. For instance, thesuspension wire 18 may be employed as a conductor connected to thenegative wire of a direct current line 14, 15. The anode is constitutedby the bodies 4 and 5 which are movably arranged, by means of suspensionwires 9 and 10 passing over rollers 6, 7 and 8, in the interior and onthe exterior respec- 7 tively of the hollow body 3. The anode 4 is Ishown as a continuous unitary solid body, but may if desired also be inthe form of a hollow body-for example, a'hollow cylinder. The wires 9and 10 can likewise serve as current conductors by connecting them tothe positive wire of the line 14, 15. On the anodes 4 and 5, the lengthof which is preferably about one-tenth of that of the hollow body, thereare arranged projections 11 and 12 of insulating material for thepurpose of obviating short-circuiting between the electrodes. Instead.of the lug-like projections shown, centeringbeads of insulating materialmay be provided on the anodes. These insulators also serve the purposeof guiding the anodes with relation to the cathodes and have the effectof maintaining a nearly constant spacing between the anodes and cathode,and consequently of maintaining a nearly constant current density at thecathode, this being of great importance inplating with chromium fromchromic acid solutions. A cock 13 arranged on the vessel 1 serves forthe introduction of fresh electrolyte. The apparatus is preferablyemployed in the following manner First, the anodes 4 and 5 are let downuntil their lower edges are approximately on a level with that of thehollow body 3. The level of the electrolyte is then preferably so chosenthat it is only at a small distance above the upper edges of the anodes.Thereupon the current is switched on by means of the switch 17 and theanodes 4 and 5 are gradually raised by means of the wires 9 and 10 by ahandle 16, connected to the wires 9, 10. Instead of the handle 16 anysuitable automatically working machinefor example a clockworkmay be usedfor the same purpose. The cock 13 is at the same time opened to such anextent that the level of the electrolyte 1s always maintained alittle-for example, a few centimetres-*above the upper edges of theanodes 4 and 5. The movement of the anodes preferably takes place at auniform velocity which is so chosen that the coating produced is of thedesired thickness.

The insulating centering pieces, which may also be secured to the upperand the lower ends of the anodes 4 and 5 (for instance 1n the form oftooth-like discs), prevent the anodes 4 and 5 as they move vertically ina straight path, from striking against the cathode 3.

In this way, the whole hollow body becomes gradually coated. It isself-evident that if a galvanic coating is to be produced only on theinterior or only on the exterior surface of a body, the particular anodewhich at the time being is not to be used, is removed from the bath.

In the new process a slight dispersion up wardly and downwardly from theedges of the anode generally takes place which results even before theactual galvanization, in the production of a coating similar to thatproduced by breathing on a surface on the parts of, the body that areencountered by the dispersed substance. The advantage of this is thatthe body is not attacked by the electrolyte and, in addition, the maincoating produced on direct juxtaposition of anode and cathode adhereswith extraordinary'firmness. It will be noted that both the inner andthe outer surfaces of the hollow body 3 are in contact with theelectrolyte, and that the liquid in the two annular zones through whichthe current passes from the anodes 4' and 5 to the cathode formed by thebody 3, is in communication with a much larger body of liquid. In thedeposition of chromium and of some other metals, considerable heat isdeveloped. This heat, which is liable to interfere with the success ofthe plating operation, is readily absorbed'by, and dissipated in, thelarge body of electrolyte in which the body 3 and both anodes 4, 5 areimmersed.

The new process is therefore especially advantageously applicable in thecase of the production of chromiumcoatings; it can, however, be employedfor the production of any other desired coatings, especially in the caseof oxidizin electrolytes and hollow bodies of easily attac able metal.

body, passing an electric current from said anode throughthe electrolyteto said body, the latter serving as a cathode, and effecting relativemovement of anode and cathode lengthwise of said hollow body, the anode,at the beginnin of such movement, being adjacent to the lbwer end ofsaid body, and adding quantities of the electrolyte to keep the level oftheelectrolyte a small distance above the upper edge of said anode.

2. The method of producing a galvanic chromium coating on a hollow body,which consists in dipping the hollow body into an electrolyte suitablefor chromium deposition, in such a manner that said electrolyte will bein contact with the inner surface and with the lower end of the saidhollow body, placing within said body an anode which is a small fractionof the length of said hollow body, passing an electric current from saidanode through the electrolyte to said body, the latter serving as acathode, efi'ecting rel ative movement of anode and cathode lengthwiseof said body, in a vertical direction, and adding such quantities ofelectrolyte that the level of the electrolyte will be ke t a smalldistance above the upper edge 0 the said anode.

3. The method of producing a galvanic chromium coating on a hollow body,which consists in dipping the hollow body into an electrolyte suitablefor chromium deposition, in such a maner that said electrolyte will bein contact with the outer surface and with the lower end of the saidhollow body as well as with the inner surface thereof, placing an anodeexteriorly of said body and an anode within such body, each of saidanodes being a small fraction of the length of said hollow body, passingan electric current through said electrolyte from said anodes to saidbody, the latter serving as a cathode, and moving said anodes lengthwiseof said hollow body from the bottom thereof to the top, and addingquantities of the electrolyte to keep the level of the electrolyte asmall distance above the upper edges of said anvanic chromium coating ona tubular body,.

comprising in combination a vessel adapted to contain an electrolytesuitable for chromium deposition and the tubular body to be coated, awire for connecting the said tubular body with the negative pole of asource of electric current, means for suspending the said tubular bodystationary in the said vessel at adistance above the bottom of the saidvessel, an anode suspended within said body, said anode being a smallfraction of the length of said hollow body, insulating means to guideand to keep said anode out of contact with said tubular body, means formoving the said anode along the inner surface of the said tubular bodyfrom the bottom to the top, and a device for introducing such quantitiesof electrolyte intothe said vessel that the level of the electrolyte inthe said vessel both within and without the said tubular body will bekept a small distance above the upper end of the said anode.

6. Apparatus for producing a chromium coating on both the outer and theinner surfaces of a tube, comprising in combination, a vessel adapted tocontain an electrolyte suitable for chromium deposition and the tube tobe coated, means for suspending the said tube in a vertical position inthe said vessel and for connecting the said tube with the negative poleof a source of electric current, an anode suspended within the saidtube, insulating means for guiding and for keeping said anode out ofcontact with said tube, a wire connected to said anode, an annular anodeexteriorly of the said tube, each of said anodes being a small fractionof the len h of-said hollow body, insulating means or guiding and forkeeping said second anode out of contact with said tube, another wireconnected to said second anode, and means adapted to move the saidanodes lon 'tudinally along the spectively. 4

7. The method of electroplating a conducting hollow bod on both itsouter and its inner surfaces, w ich consists in dipping it into anelectrolyte in such a manner is said surfaces of the body will be incontact with the electrolyte, placlng two anodes each of relativellysmall length com ared with that of said bo adjacent to said ody, oneinteriorly and other exteriorly thereof, efiectinner and the outer suraces of the tube reat both of ing relative movement between said anodesand said body, and passing an electric current through the electrolytefrom said anodes to said body, the latter serving as a cathode.

8. Apparatus for electroplating conducting hollow bodies both on theirinner and on their outer surfaces, comprising a vessel adapted tocontain an electrolyte and the body to be plated, two spaced anodes solocated that the article to be coated may be placed between them, saidanodes each being of a length which is relatively small as compared withthe height of said vessel, connections for causing an electric currentto pass through the electrolyte from said anodes to said body, and meansfor effecting relative longitudinal movement between said anodes andsaid body.

9. Apparatus for electroplating conductinghollow bodies both on theirinner and on their outer surfaces, comprising a vessel adapted tocontain an electrolyte and the body to be plated, two spaced anodes solocated that the article to be coated may be placed between them, saidanodeseachbeingofalen'gth which is relatively small as compared with theheight of aid vessel, connections for causingan electric current to passthrough the electrolyte from said anodes to said body, and insulatingmeans carried by each anode and projecting therefrom toward the otheranode to prevent contact of said body with either anode, and to guidethe latter.

tures.

VICTOR ENGELHARDT. KURT ILLIG.

In testimony whereof we aflix our signa-

